Tar product



Planted Feb. 1,

TAR PRQDUCT Deric William Parkes, West Bromwich, England, assignor to The Midland Tar Distillers Limited, Oldbury, Birmingham,

company England, a British No Drawing. Application October 16, 1941, Se

rial No. 415,213. 1940 2 Claims.

This invention relates to tar products and their manufacture, and the principal object is to provide improved colored tar and an improved way of making it.

Another object of this invention is to produce colored tar of good weathering properties and good color stability.

The refined tar" usually used in binding road surfaces is produced by distilling crude tar to leave a pitch which is then oiled back," that is to say, mixed with oil to give a product of the desired viscosity.

This product contains matter which is insoluble in various solvents. In particular it contains matter which is insoluble in toluene and which is generally called free carbon, although this term is a misnomer, as the fraction in question can be separated into two sub-fractions, namely that which is insoluble in pyridine (usually known as C1) and that which is soluble in pyridine (usually known as C2). The C1 fraction approximates to pure carbon and is in suspension in the refined tar. It is generally regarded as being a fine filler in the tar, the presence of which confers no special properties on the tar. The C2 fraction is in solution in and is commonly accepted as a valuable binding constituent of the refined tar and its presence is considered to be advantageous.

The amounts in which these two fractions are present are increased by heat treatment, and therefore by the normal distillation of crude tar. They are also increased to some extent during natural weathering, particularly when the tar is exposed to ultra-violet light.

I have come to the conclusion that these increases in the C1 and C2 content of the tar are largely instrumental in causing refined tar to become brittle and therefore in decreasing its life.

The invention is based on this conclusion and on the discovery which I have made that refined tars from which both the C1 and 02 fractions have been removed have weathering properties which are far better than those of most normal refined tars in spite of the fact that the removal of these fractions involves the removal of matter which is known to confer good binding properties on the tar. I have further discovered that refined tars from which the C1 and C2 fractions have been removed are much lighter in color than the usual refined tar, and therefore are suitable bases for the manufacture of colored tar products by the addition to them of an appropriate pigment. What is, perhaps, still more In Great Britain January 19,

important is thatthese tar products are reasonably color-stable, that is to say, they retain their original color for an appreciable length of If a colored tar product is required, pigments are added to the binder either before or during the mixing of the binder with the aggregate.

In carrying out the invention, crude tar may first be distilled to remove water and part of the oil content. The pitch that forms the resi: due may then be extracted with a solvent in which the C1 and C2 fractions are insoluble, and the solvent may be removed by distillation. There are a number of suitable solvents from which to choose. The best'are naphtha, particularly heavy coal tar naphtha, kerosene and white spirit. In general, the solvent extraction process will be carried out hot. Thus, the product obtained by dehydration and distillation of the crude tar can suitably be heated to from 100 to 110 C. and have added to it a: quantity of naphtha at a temperature of 55 to 85 C. When this is done, a bituminous mass containin the C1 and C2 fractions separates out. The extract is separated and is cooled and allowed to settle. As a result, a resinous substance is thrown down. For the complete separation of this resinous substance, 8. period of several days is generally needed. The bulk of it separates out, however, in from 18 to 24 hours. It is advisable to remove as much of this resinous substance as possible because its presence is apt to dull the final color of the tar binder. The

' extent to which it is removed, if at all, will by this method naturally depend upon which is aimed at.

The clarifiedextract is distilled for the removal of the solvent and the residue is oiled back in the usual manner to the required viscosity.

The amount of binder which can be extracted depends, of course, upon the nature of the starting material. Hard pitches extracted with naphtha are generally found to yield only about 30% of their weight as extract, whereas a medium soft pitch may yield as much as 50%.

For oiling back the extract, any of the usual oils can be used. Clean creosote is very suitable, but where the best weathering properties the particular result ment and parts of titanium are to be obtained, the high-boiling oils obtained by distilling medium soft pitch are preferred.

The removal of the C1 and C2 fractions can be effected otherwise than by the use of a solventextraction process. One very successful method is to distill or coke pitch produced from crude tar and to separate from the remainder of the distillate (or product driven off in the coking oven) the later fraction, which has the consistency of soft pitch. This fraction when formed devoid of the C1 and C2 fractions (which are left behind as residue in the distillation) and when oiled back with a suitable oil to the required viscosity has very good Weathering properties and is of light color.

The binder in accordance with the invention can be usefully used for the manufacture of colored tar macadam. For example, the aggregate can be heated to from 70 to 80 C. and may have the tar binder applied to it at about the same temperature. If the coloring matter is then added, it is found to disperse readily over the coated aggregate. The coloring matter may, however, be added to the binder before the latter is applied to the aggregate.

Good results have been obtained by applying 26 lbs. of the tar binder to 500 lbs. of aggregate and adding thereto 5 lbs. of titanium white pigment. A brown produced.

To obtain a green macadam, 20 lbs. of a green pigment may be used. It is found advantageous in this and other cases to use a small amount, for example 3 or 4 lbs., of titanium white in addition to the other pigment, because the white helps to bring out the other colors.

The tar binder produced in accordance with the invention can be used for all the purposes to which ordinary refined tar is applied. Thus, it can be used for coloring chips to be applied to road surfaces which have been treated with a tack coat of ordinary tar. It can also be used in the form of a paint which can be applied by spraying or brushing. A suitable product for this purpose has been obtained by dissolving 25 parts of the extract obtained from medium soft pitch in 12 parts of a solvent consisting of equal parts of xylol and benzol. A. green paint has been successfully used consisting of such a base to which has been added 20 parts of green pigoxide. When used, this paint was found to be surface-dry in from one to two hours.

It will, of course, be appreciated that it is not entirely essential to remove the last traces of the C1 and C2 fractions, especially when only dull colors are required. The degree to which the removal is effected will naturally depend upon the use to which the final product is to be put and upon the price at which the material is to be manufactured. The more that is removed, the better will be the weathering properties and the lighter the color of the final product.

Some practical examples are as follows:

coloured macadam is thus Example 1 2350 lbs. of medium soft pitch having a melting point of 762 C. (ring and ball) were mixed with the naphtha to the powdered pitch, and heating to to C. when the rest of the naphtha heated to 55 to 85 could be rapidly mixed in. After stirring vigorously, the whole was allowed to settle, when the C1 and C2 fractions settled out as a pasty mass. The naphtha extract was then separated at a temperture of about 60 C. and allowed to cool. As a result, it deposited a quantity of dark coloured resin. To the extract were now added 746 lbs. of heavy creosote distilling substantially between 270 and 360 C. and the whole was transferred to a still Where the solvent naphtha was removed. The finished product amounting to 188 gallons (2104 lbs.) had a viscosity of 62 seconds B. R. T. A.) at 30 C.

The excellent weathering properties of this material as a road binder are shown by the fact that its critical temperature after oxidation (C. T. 0.) measured by means of the rubber strip test was only 45 C. at 72 hours weathering whereas an ordinary tar of similar viscosity made from the same raw materials had a C. T. O. of 55 to 60 C. The rubber strip test is described in Chemistry 8: Industry" June 17, 1939, Vol. LVIII, No. 24, pp. 565-572.

This binder was satisfactorily used for making a green tarmacadam thin carpet which was laid on a concrete aerodrome runway in the usual way.

The colored macadam mixture was prepared in the usual way by coating 2240 lbs. of the hot aggregate with 112 lbs. of the binder and adding 29 lbs. of green pigment and 25.6 lbs. of white pigment. The time required for mixing was a few minutes longer than is usually required for a black tarmacadam'mix.

Example 2 91 parts of the later part of the distillate obtained in coking pitch and having a viscosity of 45 seconds at 37 C. were mixed with 9 parts of heavy naphtha previously referred to. The product had a viscosity of 11 seconds at 30 C. It was used for making green pre-coated chips, 15 parts of binder being mixed with 500 lbs. of hot 1%" granite chips, 5.25 lbs. of green pigment being finally. added. When cold, the chips were dry and non-tacky and of a useful green color.

The production of a colored tar product having good weathering properties and good color stability is a matter of special interest at the present time because it provides a very effective method of camoufiaging surfaces which normally stand out very prominently indeed, for example, the surfaces of aerodrome runways, main roads, and so on. Colored tar products and road materials are, of course, also required for purely decorative purposes and other purposes of a nonmilitary nature.

I claim:

1. A tar binder consisting of a pitch residue of coal tar from which toluene insoluble fractions have been wholly or substantially removed, said pitch oiled back with a relatively high boiling oil to a consistency suitable as a binder.

2. A tar binder consisting of a pitch residue of coal tar from which constituents insoluble in toluene have been wholly or substantially removed, said pitch oiled back with a relatively high boiling oil to a consistency suitable as a binder and containing a pigment.

DERIC WILLIAM PARKES. 

